A recent trend in automobile drive technology, as part of developments in the automobile electronics sector, is for established passive safety systems like seatbelts and airbags to be extended by active safety systems, such as anti-lock braking systems (ABS), electronic stability programs (ESP) and electrical steering systems, to provide an increasing range of driver assistance functionalities. As has already been the case in the drive train for some time, system complexity is also continuously increasing here in order to detect hazardous driving situations and contribute to accident avoidance through active interventions by a control system. With ongoing technological advances, these trends are expected to continue and grow stronger in the future.
The resulting significant increase in the number of electronic components with a safety-related functionality has given rise to previously unprecedented requirements in terms of reliability and system availability. In order to be able to achieve this while at the same time meeting cost objectives, it is desired to develop efficient methods for functional self-monitoring through integrated test methods along with redundancies. At the same time, progress is desired in design methodologies in order to be able to identify and avoid possible weaknesses in safety systems early on. In the area of magnetic field sensors, for example, this has been done by the introduction of the Safety Integrity Level (SIL) standard.
In order to meet SIL standards in the automotive field, it is desired to implement and use corresponding self-tests, including built-in self-tests, not only at start-up but also during normal operation, as well as automatic monitoring structures or corresponding redundant functional blocks and/or signal paths. Conventional magnetic sensor systems, in particular linear Hall measuring systems, have used a single-channel analog main signal path. It is technically very difficult, or perhaps even impossible, to meet the SIL requirements in safety-critical applications with this concept. It is therefore no longer possible to cover safety requirements with just one sensor system. Thus, other conventional solutions have used two identical redundant magnetic field sensors to meet SIL requirements. Obviously, a considerable drawback of these solutions is the corresponding doubling of the cost for not one but two sensors. Still other solutions propose a defined superimposed test signal outside the signal frequency rages, such as magnetic field sensors with an additional on-chip conductor loop or pressure sensors with superimposed electrostatic coupling to the sensor.
A need remains for a reliable and cost-efficient sensor system that meets SIL and/or other applicable safety standards.